Field of the Disclosure
The present disclosure generally relates to image forming and, more particularly, to an image forming apparatus such as an electrophotographic copier, printer, facsimile apparatuses, or the like.
Description of the Related Art
An electrophotographic image forming apparatus in the past performs an operation for charging an image bearing member such as a photosensitive member and an electrostatic recording dielectric substance by discharging. Technologies such as corona electrical charging and contact electrification have been known for charging an image bearing member by discharging. In particular, contact electrification has often been adopted in recent years because of its advantages of low ozone generation and low power consumption. According to the contact electrification, voltage equal to or greater than discharge start voltage is applied to a charging member in contact with an image bearing member so that a surface of the image bearing member can be charged by discharging occurring in a minute void between the image bearing member and the charging member. As the charging member, a charging roller that is a roller-shaped member has been used widely from a viewpoint of high charge stability.
Such a scheme which charges an image bearing member by discharging may generate a discharge product such as ozone and NOx, and the discharge product attaches to a surface of the image bearing member. The contact electrification produces a lower amount of discharging and generates a less discharge product, compared with corona electrical charging using a corona charger. However, because, according to the contact electrification, a discharge product occurs at a minute void between an image bearing member and a charging member, the discharge product attaches to a surface of the image bearing member even if the occurring discharge product is less. When a discharge product is attached to a surface of the image bearing member, the discharge product absorbs moisture and reduces resistance of the surface of the image bearing member, which thus reduces the charge holding capacity of the image bearing member. This may cause a phenomenon called “image smearing” resulting in a defective electrostatic latent image by missing, blurring and smearing.
In order to reduce such an influence of the discharge product, methods have been known which will be described below. For example, a heater placed inside or neighboring to an image bearing member may be used to increase the temperature of a surface of the image bearing member and thus to dry the surface of the image bearing member. Alternatively, an image bearing member may be rotated during a non-image-forming period to increase the number of times of friction per unit time period between the image bearing member and a cleaning member to remove the discharge product. Further alternatively, abrasives may be supplied to a surface of the image bearing member for improved polishing capability of the image bearing member with a cleaning member. Further alternatively, a release agent for improved releasability may be supplied to a surface of an image bearing member to prevent a discharge product from easily attaching to the surface of the image bearing member.
Operations for reduction of such influences of a discharge product may be desirably executed in a state that image smearing easily occurs for suppression of consumption of energy and materials more than necessary, wearing of components, and reduction of image productivity. Image smearing may easily occur when, for example, an image forming apparatus is installed in a high temperature with high humidity environment that is harsh for printing operations over a long period of time. Accordingly, a technology has been proposed which detects a state where image smearing may easily occur and executes operations for reducing influences of a discharge product as described above.
Japanese Patent Laid-Open No. 2010-113103 proposes a method for detecting a state that image smearing may easily occur based on a fact that an image bearing member is slightly charged in a case where direct current voltage lower than discharge start voltage is applied to a charging member when a discharge product is attached to a surface of the image bearing member. This method can be implemented by providing a detection circuit configured to detect an electric current value or a voltage value when direct current voltage lower than discharge start voltage is applied to a charging member, without requiring a potential sensor configured to detect a surface potential of the image bearing member around the image bearing member, which can advantageously reduce the size and costs of an apparatus to be applied.
Here, the detection method in the past if adopted is desirably implemented by using a minimum necessary detection circuit from viewpoints of reduction of the size and costs of an apparatus to be applied. However, in a case where the conventional detection method is applied to a tandem type image forming apparatus having a plurality of image bearing members and where the plurality of image bearing members share such a detection circuit, it may be difficult to distinguish each of the image bearing members and to detect which of them has a state that image smearing may easily occur. Japanese Patent Laid-Open No. 2010-113103 does not give any suggestion with respect to the point.